1. Field of the Invention
The present invention relates to a detection device and detection method for detecting a repeat field in a telecine image transformed into 60 fields by 32-pull down, and more particularly to a detection device or the like for detecting a 32-pull down sequence at high reliability.
2. Description of the Related Art
When an image (cinema image) based on a 24 frame progressive scan is transformed into an image (telecine image) based on a 60 field interlace scan, a transformed processing called a 32-pull down has been conventionally used.
The 32-pull down transforms the cinema image into the telecine image by repeating a field two fields before once every five fields (e.g. Japanese Patent Application Laid-Open No. 2002-354431).
By this, the cinema image recorded on a DVD (Digital Versatile Disk) can be transferred to a display device as NTSC type TV signals, and the cinema image can be transmitted from a broadcast station as NTSC type TV signals.
In the case of displaying the 60 field telecine image transferred from the DVD, or transmitted from the broadcast station on the 60 frame progressive type display device, the 32-pull down sequence is detected (particularly the field repeated by 32-pull down sequence (hereafter called “repeat field”) is detected), and the interlace image is transformed into the progressive image (IP (Interlace to Progressive) transform).
In the IP transform, the 60 fields telecine image is transformed into the original 24 frame progressive image, by deleting the detected repeat fields, for example. And the telecine image is transformed into the progressive image by repeating two frames and repeating three frames for every other frame.
FIG. 12A and FIG. 12B are diagrams depicting a system configuration example when IP transform is performed, and the telecine image is displayed on the display device as the 60 frame progressive image.
FIG. 12A is a diagram depicting a system configuration example when the telecine image regenerated from a DVD is IP-transformed by a DVD player 100, and is displayed on a display device 110.
The DVD player 100 has a decoder 101 for decoding the telecine image encoded by compression, for example, and a converter 102 for IP-transforming the decoded telecine image. The repeat field is detected in the converter 102.
FIG. 12B is a diagram depicting a system configuration example when the telecine image transmitted from the broadcast station 120 is IP-transformed and displayed on display devices 140 and 150.
The broadcast station 120 has a converter 121 for performing 32-pull down transform, and an encoder 122 for encoding, such as compression.
By the converter 121, the cinema image is transformed into the telecine image, and is output to a display device 150 in a home as an analog broadcast. The telecine image is encoded by compressing, for example, by the encoder 122, and is output to the display device 140 via an antenna 130 as a digital broadcast.
IP transform is performed by the decoder 131 on the display device 140 in the case of the digital broadcast, and is performed by the display device 150 in the case of the analog broadcast.
In IP transform, it is critical to detect repeat fields. Conventionally the difference value of each pixel between adjacent fields is determined for the telecine image which is input, and this difference value is compared with a redundant threshold and a non-redundant threshold (e.g. Japanese Patent Application Laid-Open No. 2002-354431).
In another prior art, the repeat field is detected by comparing a cumulatively added difference value with a threshold value for each field period (e.g. Japanese Patent Application Laid-Open No. H10-65964).
However in the case of detecting repeat fields according to Japanese Patent Application Laid-Open No. 2002-354431 and No. H10-65964, if the telecine image broadcasted from the broadcast station is IP-transformed, for example, the progressive image cannot be displayed at high image quality because of the influence of noise.
In the example in FIG. 12B, noise is generated in the received telecine image because of the influence of air in the case of the analog broadcast. In the case of the digital broadcast, the telecine image before encoding cannot be perfectly regenerated by decoding because of the encoded noise. This problem in particular is conspicuous if encoding is a lossy transform.
Also the characteristics of noise greatly differs between the case of performing IP transform by the DVD player (see FIG. 12A), and the case of performing IP transform of an NTSC signal from the broadcast station (see FIG. 12B), and repeat fields cannot be detected.